AR0130 Datasheet, PDF (24/53 Pages) ON Semiconductor – CMOS Digital Image Sensor

AR0130: 1/3-Inch CMOS Digital Image Sensor
Features
Maintaining a Constant Frame Rate
Maintaining a constant frame rate while continuing to have the ability to adjust certain
parameters is the desired scenario. This is not always possible, however, because register
updates are synchronized to the read pointer, and the shutter pointer for a frame is
usually active during the readout of the previous frame. Therefore, any register changes
that could affect the row time or the set of rows sampled causes the shutter pointer to
start over at the beginning of the next frame.
By default, the following register fields cause a “bubble” in the output rate (that is, the
vertical blank increases for one frame) if they are written in video mode, even if the new
value would not change the resulting frame rate. The following list shows only a few
examples of such registers; a full listing can be seen in the AR0130 Register Reference.
• x_addr_start
• x_addr_end
• y_addr_start
• y_addr_end
• frame_length_lines
• line_length_pclk
• coarse_integration_time
• fine_integration_time
• read_mode
The size of this bubble is (Integration_Time × t_ROW), calculating the row time according
to the new settings.
The Coarse_Integration_Time and Fine_Integration_Time fields may be written to
without causing a bubble in the output rate under certain circumstances. Because the
shutter sequence for the next frame often is active during the output of the current
frame, this would not be possible without special provisions in the hardware. Writes to
these registers take effect two frames after the frame they are written, which allows the
integration time to increase without interrupting the output or producing a corrupt
frame (as long as the change in integration time does not affect the frame time).
Synchronizing Register Writes to Frame Boundaries
Changes to most register fields that affect the size or brightness of an image take effect
on the frame after the one during which they are written. These fields are noted as
“synchronized to frame boundaries” in the AR0130 Register Reference. To ensure that a
register update takes effect on the next frame, the write operation must be completed
after the leading edge of FV and before the trailing edge of FV.
As a special case, in single frame mode, register writes that occur after FV but before the
next trigger will take effect immediately on the next frame, as if there had been a Restart.
However, if the trigger for the next frame occurs during FV, register writes take effect as
with video mode.
Fields not identified as being frame-synchronized are updated immediately after the
register write is completed. The effect of these registers on the next frame can be difficult
to predict if they affect the shutter pointer.
AR0130 DS Rev. L Pub. 6/15 EN
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©Semiconductor Components Industries, LLC, 2015.